There are numerous Mathematics blogs out there!
A really easy way to follow the UK education Maths blogs is to follow The Maths Echo Chamber
Try Mathblogging.org to see recent posts from an extensive collection of blogs from around the world about mathematics in all its facets.
Craig Barton who has included some of his own favourite blogs in the video at the end of this post (thank you for the mention Craig!) has now set up his own blog where you will find many excellent TES resources; see for example all the Top 10 Collections and the Resource of the Week. See also Craig’s examples from his fantastic Diagnostic Questions site.
And whilst not strictly Mathematics blogs these personal favourites on Teaching and Learning and more by many excellent writers have something to say for teachers of any subject.